Problem: The enthalpy of formation (ΔHf) of rubidium chloride is -430.5 kJ/mol. The enthalpy of sublimation for rubidium is 86 kJ/mol, and the first ionization energy of rubidium is 402 kJ/mol. The bond dissociation energy of (g) is 243 kJ/mol, and the electron affinity of chlorine is -349 kJ/mol. Calculate the lattice energy of RbCl (s), in kJ/mol.a. -170b. -691c. +260.5d. -812..5e. -260.5

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We’re being asked to calculate the lattice energy of rubidium chloride (RbCl)


Recall that lattice energy is the energy required to combine two gaseous ions into a solid ionic compound:


Mx+(g) + Ny–(g)  MyNx(s)


To calculate for lattice energy, we need to do the Born-Haber cycle for RbCl


We start with the corresponding formation equation for RbCl:

Rb(s) + 1/2 Cl2(g)  RbCl(s), ΔH˚f


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Problem Details

The enthalpy of formation (ΔHf) of rubidium chloride is -430.5 kJ/mol. The enthalpy of sublimation for rubidium is 86 kJ/mol, and the first ionization energy of rubidium is 402 kJ/mol. The bond dissociation energy of (g) is 243 kJ/mol, and the electron affinity of chlorine is -349 kJ/mol. Calculate the lattice energy of RbCl (s), in kJ/mol.

a. -170

b. -691

c. +260.5

d. -812..5

e. -260.5